What Kind of Sound Insulation Can I Use Under Solid Hardwood Flooring?

Installing hardwood floor
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Solid hardwood floors are among the best of all flooring materials, but they come with one notable drawback—the density of sold hardwood floors mean that they easily transmit sound vibrations. In a two-story house, it's common to be able to hear the noise of people walking overhead on hardwood floors. Homeowners have tried many solutions to this problem, and many make the mistake of using the same foam underlayment padding that is designed for laminate flooring or floating engineered wood flooring. There are, however, some solutions that are recommended by flooring manufacturers and installation professionals, described here. 

With Nail-Down or Glue-Down Flooring, Use an Underlayment

  • Red rosin paper or builder's felt. These materials are the traditional underlayment that is installed between the hardwood flooring and the subfloor. These materials do help minimize squeaking between the bottom of the floorboards and the top of the subfloor, but they do not actually absorb sound, nor do they make the surface any softer to walk on, in the way that foam padding does with laminate flooring. You can, however, install double- or triple-layers of paper or felt under your hardwood floor, which may help to deaden sound somewhat. 
  • Solid underlayment:  You can put down a solid (non-foam) underlayment that is specially designed for absorbing sound. SoundEater, made by Impacta, is described as a "free floating underlayment designed for nail down hardwood flooring." In this case, the underlayment does not need to be nailed to the subfloor, but the hardwood planks will be nailed down to the underlayment. 
  • A rubberized membrane. One such product is Proflex90,  a rubberized membrane with reinforcing fabric on one face. This is not a foam material, but rather a peel-and-stick rubberized fabric sheet product that is perfect for finished hardwood floors. This membrane is waterproof and eliminates cracks; and it offers a notable reduction to the sound-transmission quality of a hardwood floor. In is installed over the plywood underlayment just before the hardwood flooring is laid. 

    Construct a Sound Isolation Layer

    A more extreme solution, but one that is perhaps the very best if you truly want to minimize sound, is to install a sound-isolation underlayment between the wooden subfloor and a layer of plywood underlayment. One such product is Privacy Ultimate Underlay, a recycled rubber product that is installed over the original subfloor and is then covered by one or two layers of plywood underlayment before the hardwood flooring is laid. This offers the best sound-proofing solution of all. 

    Glue, Don't Nail

    Some types of hardwood flooring have the option of being nailed or glued down. Because metal nails act as small sound-transmission rods, your floor will be quieter if you can glue it down instead. 

    Choose a Denser Hardwood

    Solid hardwood itself does a remarkably good job of absorbing sound. Of all the types of flooring you can install, it is the best in that respect.  Within the category of solid hardwood, dense exotics like mahogany or Brazilian cherry provide better sound absorption than less-dense domestics such as oak or maple.

    Underlayment for Floating Hardwood Floors

    floating floor is one that does not need to be nailed or glued down. These products are not solid hardwood, but are instead engineered products with a thin layer of solid hardwood bonded to filler layers. These, too, can be susceptible to noise transmission, but manufacturers often provide a resilient underlayment product that will help level and cushion floors, and which also help with sound transmission. One such product is Impact Barrier Flooring Underlayment, a very efficient noise blocker that also has a membrane to resist moisture, mold, and mildew. 

    Use Rugs and Runners

    Adding fabric rugs and runners will go a long ways toward eliminating the sounds of footsteps on hardwood floors overhead.  They have the added benefit of protecting hardwood surfaces against wear and tear.